title: Parity and risk of colorectal cancer: a dose-response meta-analysis of prospective studies.
abstract: BACKGROUND
  Association between parity and colorectal cancer (CRC) risk has been investigated by several epidemiological studies but results are controversial, yet a comprehensive and quantitative assessment of this association has not been reported so far.
  
  
  METHODS
  Relevant published studies of parity and CRC were identified using MEDLINE, EMBASE and Web of Science databases through end of April 2013. Two authors independently assessed eligibility and extracted data. Eleven prospective studies reported relative risk (RR) estimates and 95% confidence intervals (CIs) of CRC risk associated with parity. We pooled the RR from individual studies using fixed- or random-effects models and carried out heterogeneity and publication bias analyses.
  
  
  RESULTS
  The summary RR for the ever parity vs. nulliparous was 0.95 (95% CI: 0.88-1.02), with no heterogeneity (Q = 9.04, P = 0.443, I (2) = 0.5%). Likewise, no significant association was yielded for the highest vs. lowest parity number (RR = 1.02, 95% CI: 0.89-1.17), with moderate heterogeneity (Q = 17.48, P = 0.094, I (2) = 37.1%). Dose-response analysis still indicated no effect of parity on CRC risk and the summary RR of per one livebirth was 0.99 (95% CI: 0.96-1.02), with moderate of heterogeneity (Q = 16.50, P<0.021, I (2) = 57.6%). Similar results were observed among all the subgroup analyses. No evidence of publication bias and significant heterogeneity between subgroups were detected by meta-regression analyses.
  
  
  CONCLUSIONS
  Results of this dose-response meta-analysis of prospective studies found that there was little evidence of an association between parity and CRC risk.
authors.affiliation: Department of Obstetrics and Gynecology, Shengjing Hospital, China Medical University, Shenyang, China.
authors.forename: Hong-Bo
authors.initials: HB
authors.lastname: Guan
authors.forename: Qi-Jun
authors.initials: QJ
authors.lastname: Wu
authors.forename: Ting-Ting
authors.initials: TT
authors.lastname: Gong
authors.forename: Bei
authors.initials: B
authors.lastname: Lin
authors.forename: Yong-Lai
authors.initials: YL
authors.lastname: Wang
authors.forename: Cai-Xia
authors.initials: CX
authors.lastname: Liu
mesh_terms: D015179:Colorectal Neoplasms / Q000453:epidemiology*; D016206:Databases, Bibliographic; D005260:Female; D006801:Humans; D016017:Odds Ratio; D010298:Parity / Q000502:physiology*; D011247:Pregnancy; D011446:Prospective Studies; D018570:Risk Assessment; D012307:Risk Factors